1. Field of the Invention
The present invention relates to an automatic transmission. In particular, the present invention relates to an automatic transmission including twin clutches hydraulically driven and controlled.
2. Description of Background Art
An automatic transmission mounted on an internal combustion engine, that includes twin clutches is known in the background art. This automatic transmission includes two clutches (first and second clutches) between a crankshaft and a gearbox. The automatic transmission is capable of sequentially shifting gears without stopping a driving force by alternately connecting and disconnecting the first and second clutches in parallel to an automatic gear shift operation by an actuator and the like. The automatic transmission including the twin clutches includes a number of gear pairs equal to the number of speeds and is configured to select which gear pair the driving force is transmitted to by connecting or disconnecting the first and second clutches and sliding a gear shift mechanism provided for a shaft rotatably supporting the gear pairs about respective axes thereof. With regard to the twin clutches, a system of selecting speeds adjacent to each other (for example, second and third speeds) by engagement of different clutches is also known in the background art.
Japanese Patent Laid-open Publication No. 8-4788 discloses a twin clutch type transmission in which twin clutches including first and second clutches are attached to one end of a crankshaft and a driving force is taken out from a double shaft connected to the twin clutches. However, in the twin clutch type transmission of Japanese Patent Laid-open Publication No. 8-4788, the first and second clutches are hydraulically controlled independently and are accommodated in a single housing. It is therefore necessary to form a complicated oil passage inside the housing and double shaft. This leads to a problem of increasing the number of production steps. Moreover, there were problems such that the total length of the oil passage is increased and a difference between distances from a hydraulic pressure source to the first and second clutches makes it difficult to attain uniform accuracy of hydraulic control.